Today, women are outliving men in every country in the world. That's right: According to the latest U.S. report, life expectancy for the ladies is 81.2 years compared to 76.4 years for males (sorry, guys!). But even though the fact that women outliving men has become widely accepted as the norm, a new study led by University of California, Los Angeles and University of Southern California researchers shows that this difference in survival rate is actually a relatively recent phenomenon, beginning just in the 20th century. (What affects your mortality risk? These 11 Things You're Doing Could Shorten Your Life.)

Focusing on mortality in adults over the age of 40, the team analyzed historical data from more than 1,700 individuals born between 1800 and 1935 in 13 developed countries. The researchers found that while mortality rates decreased for both sexes throughout the 19th and 20th centuries, female death rates began decreasing a whopping 70 percent faster than those of males after 1880.

"As infectious disease prevention, improved diets, and other positive health behaviors were adopted by people born during the 1800s and early 1900s, death rates plummeted, but women began reaping the longevity benefits at a much faster rate," the press release explained.

The biggest culprit for this surge of death rates for men? Heart disease, the study concludes. Even after accounting for deaths due to smoking, cardiovascular disease appears to still be the leading cause of most preventable deaths in men over 40.

“I was very surprised when I looked at the divergence as we got closer to the 1900s. The common belief was that this pattern would be there even in the 1800s, but it wasn't,” explained lead study author Hiram Beltrán-Sánchez. “Since our biology hasn’t changed over the last one hundred years, we realized there must be some other reason that men are dying at higher rates.”

That other reason? Lifestyle. The increasing rates of cardiovascular disease in men is attributed to health-related behaviors, in particular smoking and a diet high in both calories and saturated fats, says Beltrán-Sánchez. While there is little evidence of biology's role in this mortality gap between the sexes, there is still a possibility that men may experience an inherent, biological vulnerability to cardiovascular disease, he adds.

It's not that men are subject to dangers that women are immune to, though, says Clyde Yancy, M.D., chief of cardiology at Northwestern Memorial Hospital. After all, across their lifetime, women and men bare the same risk of heart disease, he explains.

Of course, you can never fully account for genetics, so it all comes down to avoiding three basic dangers that we can control: avoid tobacco, diets high in saturated fat, and inactivity. And that's advice for the ladies: “Today’s woman is at risk of replicating the history of yesterday’s man by being exposed to these negative influences," Yancy adds. (Check out the American Heart Association's "Life's Simple 7" to get your own health score, and find outWhy the Diseases That Are the Biggest Killers Get the Least Attention.)